Coroutines and Yield - Unity 3 Game Development - page 322

In this case, it's more convenient to use the yield statement. The yield statement is a
special kind of return that ensures that the funcion will coninue from the line ater the
yield statement the next ime it is called. The result would be something similar to the
following code.
Example
function Start() {
while (true) { //Use this line instead of Update()
//do step 0
Debug.Log("Do step 0");
yield; //wait for one frame
//do step 1
Debug.Log("Do step 1");
yield; //wait for one frame
}
}
The preceding code will have a similar result without having a new variable and an extra if
statement to check for each step event.
You can also pass special values to the yield statement to delay the execuion of
the Update funcion unil a certain event has occurred, such as WaitForSeconds ,
WaitForFixedUpdate , Coroutine , and StartCoroutine .
You can't use yield from within Update or FixedUpdate ,
but you can use StartCoroutine to start a funcion that can
use yield .
WaitForSeconds
Suspends the coroutine execuion for the given amount of seconds.
WaitForSeconds can only be used with an yield statement in coroutines .
Example
function Start() {
// Prints 0
Debug.Log (Time.time);
// Waits 5 seconds
yield WaitForSeconds (5);
// Prints 5.0